1. Field of the Invention
This invention relates generally to cardiopulmonary resuscitation (CPR), and more particularly, to a device for performing CPR through alternating active compression and decompression of the thorax and abdomen.
2. Description of the Related Art
There are approximately 550,000 cases annually of cardiac arrest in the U.S. Despite advances in many other areas of medicine, the survival rate for these cases remains low. In general, for the victims to survive, it is essential that they receive proper resuscitation as soon as possible after the cardiac arrest. It is generally felt that in order for a victim to stand a reasonable chance for survival successful cardiopulmonary support must be established within ten minutes of cardiac arrest. Beyond this, any delay in providing support is likely to result in severe brain damage.
There are two general classes of cardiopulmonary support: invasive and non-invasive. Examples of invasive support devices include percutaneous bypass, direct coronary perfusion, the Anstadt cup, hemopumps, and intraortic balloon pumping. Of course since these techniques require the insertion of devices into the body, they can only be performed by trained medical personnel. In fact, these techniques are generally not suited for emergency life support outside a hospital. Even then, they generally take longer to establish than a person in cardiac arrest can ordinarily tolerate.
Non-invasive devices tend to be easier and less expensive to use and faster to implement than the invasive equipment. Non-invasive support techniques include cardiopulmonary resuscitation (CPR), leg compression, and THUMPER.RTM. devices or compression vests which mechanically compress the chest to simulate CPR. Traditional CPR provides cardiac support through a series of rhythmic compressions of the victim's thorax alternating with mouth-to-mouth ventilation. Thoracic compression is achieved by having the care giver place his or her hands on the victim's chest and pressing down. After compression has been achieved, thoracic pressure is released and mouth-to-mouth ventilation follows. The principle advantage of CPR is its relative simplicity. An individual can be trained to administer traditional CPR in only about 15 hours.
However, traditional CPR has its limitations. For one thing, it is tiring to administer. In addition, it is not very efficient, ordinarily providing insufficient cardiopulmonary support to sustain the patient until professional emergency medical care can be provided.
The THUMPER.RTM. devices and compressive vests now used for non-invasive life support have been designed to duplicate the movements used to perform CPR, the idea being to provide a mechanical substitute for a person trained to administer CPR. Examples of such devices can be found in U.S. Pat. No. 3,219,031, No. 3,509,899, No. 3,896,797, and No. 4,397,306. Each of these patents describe devices which use a reciprocable plungers to compress a victim's chest along with a means of ventilating the victim, such as a source of pressurized oxygen or a squeeze bag. However, such devices, because they are fairly complex and not easily used by untrained lay persons, are in fact less-than-ideal substitutes for a trained CPR administrator. Furthermore, they do not improve the hemodynamic efficiency of CPR.
As an alternative to the use of mechanical chest compressors, U.S. Pat. No. 2,071,215, No. 4,424,806 and No. 4,928,674 describe how to support the pulmonary and/or cardiac functions by providing an inflatable bladder around the patient's chest. In some cases, a stiff outer shell or biasing cuff surrounds the bladder so that when the bladder is periodically inflated, the patient's chest is compressed, causing expiration and inspiration.
Because none of the commercial embodiments of these devices is entirely satisfactory, CPR remains the most common resuscitative technique used by lay persons to treat cardiac arrest.
As indicated above, traditional CPR involves the use of the administrator's hands on the victim's chest followed by mouth-to-mouth ventilation. Compressing the thorax causes blood to circulate while the mouth-to-mouth ventilation ventilates the lungs. Recently certain hand held devices have been employed to serve both these functions. Indeed, the popular media have reported on the use of a suction cup plunger, often referred to as a "plumber's helper", having been used to provide enhanced CPR.
A recent study determined that where cardiac support is provided by rhythmic chest compressions, cardiac output can be significantly improved by alternating chest compressions with chest decompressions. In this study, the chest was compressed and decompressed using a rubber plunger which alternately applied pressure and suction to the patient's chest. See Cohen, T. J., et al., "Active Compression-Decompression: A New Method of Cardiopulmonary Resuscitation", J. Am. Med. Assoc. Vol. 267, No. 21, pp. 2916-23, 1992. This technique is known as active compression-decompression CPR ("ACD CPR").
ACD CPR is reported as being significantly more effective than conventional "compression-only" CPR. It provides both perfusion and ventilation, and can resuscitate some patients where conventional CPR and defibrillation fail.
Devices capable of being used to perform ACD CPR are also described in U.S. Pat. No. 5,295,481 and European Patent Application No. 92303367.4 (Publication No. 0 509 773 A1). Each of these patents shows a device which includes a suction cup and handle. In each case, the aid giver would grab the handle and alternately press down and then pull up. The downward pressure would force air out of the lungs and blood out of the heart while the pulling up on the handle would cause the suction cup to draw the chest upwardly to pull air into the lungs and blood into the heart.
Although the traditional manner of performing CPR involves only the thorax, it has also been suggested that simultaneous involvement of the abdomen might prove even more advantageous. In an article entitled "Optimization of Coronary Blood Flow During Cardiopulmonary Resuscitation (CPR)" by Lin et al. (IEEE Transactions on Biomedical Engineering, Vol. BME-34, No. 6, Jun. 1987) the authors describe a computer simulation of CPR. Based on that simulation they conclude that coronary blood flow could be significantly improved if, in addition to alternating positive and negative pressure on the thorax, negative and positive pressure could also be applied to the abdomen. In other words, their computer model suggests that when positive pressure is applied to the thorax, it should be accompanied by the application of negative pressure to the abdomen and, conversely, as negative pressure is supplied to the thorax, positive pressure should be applied to the abdomen. The Lin et al. paper, however, appears to be based solely on the authors' computer simulation, and no structure is suggested for applying these alternating positive and negative pressures.
As previously noted, emergency medical personnel have available to them a number of different ways to treat cardiac arrest. However, none of these techniques is entirely satisfactory. Thus, there is a need for a CPR resuscitation device which is simple, easy to use, and not harmful to patients. In particular there is need for such a device which will facilitate alternating application of positive and negative pressures on the thorax and abdomen.